1. Field of the Invention
The present invention relates generally to a blood glucose monitoring method and device, and more particularly pertains to such a blood glucose monitor which can be constructed as an implant or as a portable device for blood glucose monitoring by a diabetic. As an implant, the glucose concentration in blood adjacent to the implant is measured, such that it is particularly useful for controlling an insulin pump for a diabetic person. The teachings of the present invention can also be used in the construction of a portable device useful for home blood glucose monitoring by diabetics in which the concentration of glucose in a drop of capillary blood is measured.
2. Discussion of the Prior Art
There are about one million insulin-dependent (Type I) diabetics in the United States. The vast majority treat their diabetes by regulating diet and exercise, and by taking one or more shots of insulin each day. Because of the many variations in life and in some cases the lack of dedication to maintaining tight control, blood glucose levels often fluctuate radically, and are responsible for a myriad of complications of the vascular and nervous systems.
Insulin pumps are a recent innovation that are gaining popularity in the treatment of diabetes. These pumps are now used by over ten thousand diabetics. Approximately one hundred of the pumps have been implanted (the majority in Germany), whereas the others are worn outside the body. Most of these pumps emit insulin continuously (twenty four hours a day) at a low-dosage (basal) rate. Before meals, the rate of insulin pumping is increased to a high dosage (bolus) rate to help metabolize food eaten during the meal. The high dosage supplement can be adjusted by the user, whereas the basal pumping rate is usually not adjusted unless a physician is consulted.
Considerable effort and money have been expended to develop a blood glucose monitoring device which automatically adjusts the rate of insulin pumping based upon the varying need of the body for insulin. This need can change dramatically from day to day and at different times within a day, depending on the level of activity and general physical and mental health of the diabetic.
Most efforts at building an implantable blood glucose monitoring device have centered on the use of a glucose oxidase enzyme electrode that measures the interaction of glucose in the blood with the enzyme glucose oxidase. These electrodes are specific for glucose and work well for several days, but deteriorate rather quickly as the enzyme becomes denatured and as antibodies and proteins in the blood clog the active working surface thereof.
The patent literature also discloses many inventions for glucose measuring instruments and implants. For instance, March U.S. Pat. No. 3,958,560 discloses a glucose sensor which utilizes a measurement of radiation through the cornea of the eye. March U.S. Pat. No. 4,014,321 is similar to the preceeding patent, but uses two frequencies of polarized radiation, and measures the optical rotation thereof. Edelman U.S. Pat. No. 4,073,292 discloses an implant which injects Benedict's solution to react with urine from kidney, and measures the transmittance of light from an LED to a photodetector, and thereby controls the insulin injection. Rao, et al. U.S. Pat. No. 4,140,963 discloses an implant with an electrochemical glucose cell, which may be of many different types to produce an electrical measurement signal.
The patent literature also dicloses many optical instruments having technical optical approaches similar to the present invention, but not involved in the measurement of blood glucose levels. For instance, Barnes U.S. Pat. No. 2,413,208 discloses a refractometer with a differential optical system, in which a prism has one surface adjacent to a liquid sample being measured and a second surface adjacent to a reference liquid, and the instrument operates at an angle just below the critical angle to enhance its sensitivity. Rando U.S. Pat. No. 3,450,476 also discloses an interferometer for measuring the index of refraction of a sample. Lubbers U.S. Pat. No. 4,306,877 discloses an instrument in which an indicator behind a permeable membrane reacts to monochromatic radiation, as by a change of color, to indicate the concentration of a substance of interest.
However, the prior art does not disclose a technical approach for measuring the level of glucose in blood similar to that of the present invention, which is suitable for construction as an implant or probe, such that it can be used for controlling an insulin pump, or as a portable device for home blood glucose monitoring.